This invention starts from a wiper installation according to the features of the preamble of the appended claims.
Often the torque of the wiper motor in wiper installations is insufficient to move the wiper blade over a dry pane. Also in the winter, when it is heavily snowing, the wiper blade and thus also the motor is blocked. In such a case the motor is subject to a considerable thermal load. In order to protect the motor against destruction thermoswitches are connected into the operating circuit, which are periodically interrupting and closing it. The motor is then energised in intermittent operation, whereby the ratio of pulse duration to pulse interval must be so small that for all that the motor is not overheated. The switching process of such thermoswitches is, however, also affected by the outside temperature, so that under certain circumstances they may be switched off too during undisturbed operation.
Besides it is difficult to realize a sufficiently big pulse interval. Until now it was therefore practiced to design the motor in a way that in case of blocking it gets over a given switching-on time without damages. This can only be achieved by a corresponding insulation of the armature winding; this, however, is very expensive.
The invention is based on the problem to develop a wiper installation of the type mentioned above in a way that in case of overload the wiper motor is reliably protected against destruction, whereby the measures necessary for this purpose are to be integrated into usual installations as economically as possible. This integration necessitates that the wiring in the motor vehicle must be retained as far as possible.